He became a creationist around 1976, and gave testimony defending creation science at the McLean v. Arkansas and Edwards v. Aguillard court cases. During the latter case, he co-authored the creation science supplementary textbook Of Pandas and People. The case decision went against teaching creation science in public schools, and the authors then altered all references to creationism to refer to intelligent design before the book was published in 1989. He subsequently became a Fellow of the Discovery Institute, and continued to endorse young Earth creationism.

In 1969, Kenyon co-authored Biochemical Predestination with Gary Steinman. Chemist Stephen Berry explained Kenyon and Steinman's theory as "describing the following causal chain: the properties of the chemical elements dictate the types of monomers that can be formed in prebiotic syntheses, which then dictate the properties of the occurring polymers, which finally dictate the properties of the first eobionts and all succeeding cells."[2] Kenyon's work was about virus production.[3]

During the 1969-1970 academic year he was "on a fellowship at the Graduate Theological Union in Berkeley, where he reviewed the contemporary literature on the relationship of science and religion."[4] Then in 1974, he was a Visiting Scholar to Trinity College, Oxford.

Kenyon states that his views changed around 1976 after exposure to the work of young earth creationists:

Then in 1976, a student gave me a book by A.E. Wilder-Smith, The Creation of Life: A Cybernetic Approach to Evolution. Many pages of that book deal with arguments against Biochemical Predestination, and I found myself hard-pressed to come up with a counter-rebuttal. Eventually, several other books and articles by neo-creationists came to my attention. I read some of Henry Morris' books, in particular, The Genesis Flood. I'm not a geologist, and I don't agree with everything in that book, but what stood out was that here was a scientific statement giving a very different view of earth history. Though the book doesn't deal with the subject of the origin of life per se, it had the effect of suggesting that it is possible to have a rational alternative explanation of the past.[5]

In 1980, the San Francisco State University Department of Biology had a dispute over Kenyon's presentation of creationism, then called "scientific creationism" in Biology module 337 Evolution.[6] At that time, Kenyon challenged anyone on the faculty to a debate on the merits of evolutionary theory versus "scientific creationism." According to SFSU biology professor John Hafernik, "There was much discussion in faculty meetings as well. Eventually the faculty voted (none opposed, seven abstentions) not to alter the description of Biology 337 to include creationism. The precedent set, in the context of the 1980 discussions, was that the Department did not support teaching creationism."[6][7]

In 1981, Kenyon was recruited to be an expert witness for the creationist side in the McLean v. Arkansas case that tested the constitutionality of Arkansas' Equal Time Legislation that mandated equal time for "creation science" and "evolution science". Kenyon flew to Arkansas to be deposed and testify during the trial. However, apparently under the influence of creationist attorney Wendell Bird (who was displeased with the defense of the creationist position by the Arkansas attorney general Steve Clark), Kenyon left town just before he was to testify:

The attorney general presented six science witnesses, two more than had testified for the ACLU, presumably on the grounds that quantity made up for evident lack of quality. There would have been more had not a serious case of disappearing witnesses set in as the second week wore on. Dean Kenyon, a biologist from San Francisco State University, fled town after watching the demolition of four of the state's witnesses on day 1 of the second week. And Henry Voss, a computer scientist from California, was rapidly withdrawn at the last minute when, in pretrial deposition, he too began to expound on things satanic and demonical.[8]

The Arkansas attorney general apparently threatened to sue Bird after this interference:

There were other witnesses for the defense who did not show up. Several scientists who had been listed as potential witnesses for the state, backed out because of what Clark termed "peer pressure."

Another state witness, Dr. Dean Kenyon, a biophysicist at San Francisco State University, mysteriously disappeared on the eve of his day in court. He had flown into Little Rock on a Sunday evening, but when one of Clark's assistants went to take his deposition he could not find him. Kenyon had checked out of the hotel and flown back home. Bird had encouraged Kenyon not to testify, although Kenyon taught evolution theory for 16 years until three years ago when he became a creationist. Bird, who is general counsel to ICR, said he attempted to get other defense witnesses not to testify after he perceived the trial as botched by Clark.

Bird said he was not trying to sabotage Clark's effort. He said he merely had told several witnesses for the state that "I don't think you should jeopardize your reputation with the way [the trial] is being handled." Clark stated he was considering legal action against Bird, whose actions, he said, were "tantamount to tampering with justice."[9]

Following the McLean ruling, which declared the teaching of "creation science" in public schools to be an unconstitutional establishment of religion, Louisiana's version of the "Equal Time" legislation was put to the test. This time, Wendell Bird was deputized by the state and ran the state's defense of the law. Dean Kenyon was advertised as the creationists' lead expert witness, however the case (which eventually became Edwards v. Aguillard when it reached the Supreme Court) was decided by summary judgment, and so never went to a full trial. Nevertheless, in written briefs and in his oral arguments, Bird relied heavily on an expert witness affidavit written by Kenyon. This affidavit is online at the TalkOrigins website. It was entered into evidence in the Kitzmiller case as evidence that Kenyon was explicitly defending "creation science"—and advocating that it be given equal time in public schools and textbooks as the "only" alternative to evolution—while at the same time working on a public school textbook, which eventually became the first "intelligent design" book, Of Pandas and People.[10]

In 1987, in Edwards v. Aguillard the Supreme Court heard a case concerning a Louisiana Law that required "creation science" be taught on an equal basis with evolution in public schools. Anti-creationists argued that this was illegal on the basis that it violated the Establishment Clause of the US Constitution. Kenyon issued an affidavit in that case, stating his support for creationism, and defining it thus:

During the Edwards v. Aguillard case, Kenyon was co-authoring with Percival Davis, a creationist school textbook entitled Of Pandas and People, which was published in 1989. After the Edwards decision, all references to "creationism" were replaced with "intelligent design", with a reference to "creationists" being replaced by "design proponents". In the history of creationism, this is the origin of the term intelligent design and the link between creationism and intelligent design.[10]

In October 1992, Kenyon was told by the chair of the SFSU Biology Department to stop teaching creationism in introductory biology courses.[11] He had been teaching creationism[12] and intelligent design "for more than ten years," which received complaints from students and some faculty.[13] Following the Chair's request, the faculty came out in support of Kenyon's academic freedom and ability to teach what he wanted without administration controlling topics.[14] After a hearing, Kenyon "won the right to teach his iconoclastic view of the evolution of life."[15][16] Kenyon claimed objections to his teaching rested on a positivist view of what constitutes legitimate science.[17]